Piezoelectric pressure indicator



Feb. 20, 1940. H. HINTZE Er Al. 2,190,713

PIEzoELEoTRIc PRESSURE INDICATOR Filed March 1'7, 1938 Patented-Peli. 20, 1940 Hans Hlntze, Dresden, and Hans Illgen, Dresden- Lanbegast, Germany, assignors to Zeiss Ikon Aktiengesellschaft, Dresden, Germany Application March 17, 1938, Serial No. 196,342

In Germany February 17, 1937 4 Claims. (CL 12S-169) The invention relates to improvements in piezoelectric pressure indicators, particularly for interna] combustion engines, and is directed to a novel combination of the piezoelectric pressure element and a spark plug.

'It is an object ofi the present invention to c ombine a piezoelectric pressure element with a spark plug and insert this structure in the customary threaded aperture provided in an internal combustion engine for the reception of a standard spark plug. In this manner it is not necessary to provide the engine to be tested with a special aperture for the pressure element oi the indicator device.

Il Another object of the invention is to provide an adapter member which ilts into the customary threaded aperture of an internal combustion engine normally receiving a standard spark plug, and attaching to this adapter member a piezoy) electric pressure element and a miniature spark plug which latter is suilicient to serve in place of thetesandard spark plug while the engine is being Still another object o f the invention is to atg5 tach the miniature spark plug in such manner on' theI adapter member that the spark gap formed between the electrodes of said small size spark plug will be positioned at the same place in the cylinder of the engine at which the spark gap of so the standard size spark plug is posiumed.

lIt is also an object of the invention to form a. unitary structure of the piezoelectric pressure element, said miniature spark plug and said adapter member, and' attaching said structure as alcomplete assembly to the engine by screwing said adapter into the standard spark plug aperture.

Other objects of the invention will be apparent or will be specically pointed out in the following description having reference to the accompanyo ing drawing which illustrates one embodiment 'of the invention:

Fig. 1 is an elevation view of the test plug oi the invention consisting of a combined piezoelectric pressure element and a miniature spark plug.

Fig. 2 is a vertically sectional view of the test plus. and Fig. 3 illustrates diagrammatically a comple arrangement for indicating the pressure in a combustion engine employing the novel test plug of the invention.

lThe test plug of the invention comprises an adapter member I provided at one end with an' exteriorly threaded portion 2 fitting in a standard spark plug aperture of an internal combustion engine'andhaving'twoboresl andlrespectivel! vquartz discs I5.

arranged at an angle with respect to'each other and communicating with each other at the outer end of the threaded portion 2. The bore 4 has an enlarged outer end provided with -a thread I for receiving the piezoelectric pressure element 5 8. The other bore 3 is threaded for receiving the threaded end of the sleeve 1 of a miniature spark plug. The outer end of the bore 3 is also enlarged vto vaccommodate the enlarged cylindrical portion of the sleeve 1 and is made suiiiciently deep so l0 that the spark gap III formed between the center electrode 8 and the body electrode 9 will be 1ocated in the same position in the spark plug aperture of the engine at which the spark gap of the normally employed standard spark plug would be 1l located. 1

The piezoelectric pressure element 6 comprises a sleeve-like casing I2 yclosed at its lower end which is threadedly connected to the yadapter member I, by a gas-prooi diaphragm I3. In the M 'interior of the casing I? are arranged two measuing discs I5 of quartz between metallic electrode discs IB. It will be noted that three electrode discs I8 are provided and that one quartz disc I5 is arranged between each two electrode $5 discs II. The electrode discs I6 are provided for conducting the electric'charges away from the The center electrode I6 receives the charge from the inner faces of the quartz Y discs II, while the two other electrodes I6 receive 90 the charges from the outer faces of the quartz Y discs. The center electrode disc II is connected with a conductor Il extending axially through the pressure element, while the other electrode discs I8 are conductively connected with the mesa tallic casing I2;

The upper end of the conductor Il is electrically insulated from the casing I2 by an insulate ing plug I9 of amber and pressure member I9 is interposed between the pile of discs Il, II and 40 the insulating plug Il. The upper electrode discs It and the pressure member I9 have each a cenuralform oirock crystaLdevelopchargesot elec` Il the total charge of electricity produced. Obvi-` ously, any desired number of quartz discs may be employed and the same be electrically connected with each other in any desired manner.

I'he pressure in the cylinder of the combustion engine is transmitted through thev bore 4 to the diaphragm which in turn acts on the body and the pile of discs I5, I6. i

Since the quantities of electricity involved are extremely small, they must be amplied before they can be used for the purpose of indicating the pressure in the engine.

Referring to Fig. 3, which illustrates diagrammatically a complete pressure indicating device, it will be noted that the piezoelectric pressure element 6 is electrically connected by a twoconductor cable 22 with an amplifier 23 the output of which is applied to one pair of the delecting plates 25 of a Braun tube 2d. The other pair of deecting plates 26 which is arranged perpendicular to the first named pair, is provided with a potential corresponding tothe po sition of the position of the piston in the cylinder or the angular phase of the crank.

The variable potential applied to the deiiect-` ing plates 2i may be produced by a piston displacement transmitter comprising a pq'tential divider in which a rotatable contact member 28 driven by the crankshaft 29 of the combustion engine 30 picks up potentials ,corresponding to the momentary position of the piston 21. A device of this type is described in the U. S. patent specification No. `2,120,100 of June 7, 1938, Serial No. 750,210, filed October 26, 1934. In the present instance the contact member 28' is moved-in a circular path over a resistance 3| wound on a plate 32 and connected to a source of direct current, which for instance may have a potential of 280 volt. It will be apparent that as the contact member 23 rotates a sinusoidally fluctuating potential will result between one end of the resistance 3| and the contact member 28 and this potential is applied'to the deilecting plates 26 by the conductors 34 and 35 respectively. The conductor v35 is connected to the brush 36 engaging a slide ring 31 which is conductively con--l nected with the contact member 28.

' The electron beam in the-Braun tube is thusv deiiected in both directions and produces a pressure-displacement diagram on the fluorescent screen 38.

What we claim is:

1. In combination, a member adapted to be secured in the spark plug aperture of an internal combustion engine, a piezoelectric pressure element, and a miniature spark plug, said member ylocation in said spark plug aperture at which the sparking gap of a standard spark plug inserted in said aperture would be positioned.

2. `In combination, a member adapted to be secured in the spark plug aperture of an internal combustion engine, a piezoelectricpressure element, and a spark plug, -said member being provided with ,two acute angularly disposed bores, one end of which being in communication with each other at one endof said member, the other ends of said bores having secured therein said piezoelectric pressure element and spark plug respectively, said spark plug extending through the entire length of the bore in which it is mounted, so that the sparking gap is positioned at the very end of the bore where the latter communicates with the other bore.

3. In combination, a member adapted to be secured in the spark plug aperture oi an internal combustion engine, a piezoelectric pressure element, and a spark plug, said member being provided With two acute angularly disposed bores, one

end oi which being in communication with each` other and also with the cylinder bore of the engine when said member is inserted in said spark plusr aperture, the other ends of said bores having secured therein said piezoelectric pressure element and spark plug respectively, said spark plug extending through the entire lengthof the bore in which it is mounted, so that the sparking gap is positioned at the very end o the bore where the latter communicates with the other bore.

4. In combination, a member adapted to be secured in the spark plug aperture of an internal combustion engine, a piezoelectric pressure element, and a miniature spark plug, said member being provided with two acute angularly disposed bores, one end of which being in communication with eachother and also with the cylinder bore of the engine when said member is inserted in said spark plug aperture, the other ends of said bores having secured therein said piezoelectric pressure element and spark plug respectively. said miniature spark plug being se cured in such a position on said member that its sparking gap will be positioned at the same 1ocation in said spark plug aperture at which the sparking gap of a. standard spark plug inserted in said aperture would be positioned.

HANS HINTZE. HANS ILLGEN. 

